This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Our initial goal was to test the hypothesis that tick saliva would have solely suppressive or inhibitory effects on the production/transcription of pro-inflammatory mediators put out by dermal cells such as blood monocytes and fibroblasts when exposed to the spirochete Borrelia burgdorferi. The following in vitro experiments were conducted in order to test our hypothesis: (1) co-culture of activated human monocytes from the THP-1 cell line with B. burgdorferi in the presence and absence of tick saliva;and (2) co-culture of human and rhesus fibroblasts with B. burgdorferi in the presence and absence of tick saliva. Cell culture supernatants from each experiment were used in cytokine ELISA and/or multiplex cytokine bead arrays. RNA extracted from THP-1 monocytes at three time points during co-culture was used in microarray experiments. Validation of microarray results was gained by independent real-time PCR experiments. Our results suggest that the current paradigm may be an oversimplification of a more complex interplay between host, vector and pathogen. Tick saliva was able not only to inhibit but also enhance inflammatory mediator production and transcription elicited by B. burgdorferi in monocytes. In rhesus and human fibroblasts it was able to elicit production of pro-inflammatory mediators even in the absence of the spirochete. Moreover, saliva effects on monocytes in some cases depended on the length of exposure to the saliva, and could switch from early inhibitory to late enhancing, and vice-versa.